Aeronautics and astronautics – Spacecraft – Attitude control
Reexamination Certificate
2000-02-11
2001-12-25
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Attitude control
Reexamination Certificate
active
06332591
ABSTRACT:
TECHNICAL FIELD
The invention relates primarily to a method of simulating on the ground the external thermal fluxes absorbed in flight by each of the external radiating components of a spacecraft such as an artificial satellite or a space probe.
The invention also relates to a spacecraft designed to enable simulation of external thermal fluxes absorbed by these external radiating components in flight without it being necessary to use a mock-up.
PRIOR ART
Spacecraft such as artificial satellites and space probes are exposed in flight to external thermal fluxes such as albedo, infrared flux from the Earth and solar flux.
To protect the onboard equipment of a spacecraft from these external thermal fluxes, it is standard practice to cover most of the exterior surfaces of its structure with a thermally insulative material. This material, commonly referred to as “super insulation”, is generally in the form of a stack of films of an insulative plastics material such as Kapton®.
Also, some of the equipment on board a spacecraft dissipates heat when in operation. This equipment requires special treatment to prevent overheating inside the spacecraft.
This treatment consists in doing everything possible to enable each equipment unit concerned to be mounted directly against the inside faces of the panels forming the outside structure of the spacecraft, a window to be formed in the super insulation in register with the equipment unit, and an external radiating component to be attached to the outside surface of the panel at the location of the window.
The external radiating components contribute to passive thermal control of the spacecraft. Their functions are to evacuate heat given off by the equipment and to minimize heating of the spacecraft due to external thermal fluxes (albedo, terrestrial infrared and solar fluxes). To this end, they radiate infrared strongly and reflect most external radiation. For example, existing external radiating components generally have an infrared emissivity close to 0.80 and an albedo and solar radiation absorption coefficient that changes from around 0.1 at the start of the mission to around 0.2 at the end of the mission.
The radiating components used on spacecraft consist of plastics material film metallized on its outside face, for example. The plastics material of the film can be poly-fluoro-ethylene propylene, Kapton®, or Mylar®. The metal is generally aluminum or silver.
When a spacecraft is designed and built, many tests are carried out to verify that it will be able to fulfill its mission for the required period of time after launch, and these tests include a spacecraft thermal equilibrium test.
The thermal equilibrium test simulates heating of the component parts of the spacecraft by external thermal fluxes that the spacecraft absorbs in flight.
A first technique known in the art for testing the behavior of a spacecraft in the presence of external thermal fluxes that it absorbs in flight consists in placing a mock-up of the craft in a vacuum chamber which is equipped with a solar simulator and is cooled to a very low temperature to simulate the space environment.
However, that technique has the drawbacks of being complicated, slow and costly, and of being unable to simulate all thermal fluxes. It is in fact limited to solar fluxes and cannot simulate the albedo and terrestrial infrared fluxes that predominate in low Earth orbit.
A second technique known in the art simulates on the ground the albedo, terrestrial infrared and solar fluxes encountered by the spacecraft in flight by installing radiating tubes for heating the outside faces of the spacecraft in a thermal test facility. However, that technique has the drawback that it cannot be used for qualification of the thermal behavior of the spacecraft. This is because its lack of protection rules out perfect reproduction of the thermal fluxes in the environment of the spacecraft.
A third technique known in the art simulates on the ground the albedo, terrestrial infrared and solar fluxes encountered by the spacecraft in flight by installing test heaters on the spacecraft, attached to the inside or outside surfaces of its radiating panels.
However, attaching test heaters to the inside face of the radiating panels generally rules out perfect reproduction of the albedo, terrestrial infrared and solar fluxes encountered by the spacecraft in flight. This is because layout constraints rule out arranging the heaters on the surface in the uniform manner that would be necessary to reproduce perfectly the thermal phenomena concerned.
Furthermore, if the test heaters are attached to the outside surfaces of the radiating panels (a technique known in the art and described in particular in the article “Clementine Thermal Design and Verification Testing: Quick, Cheap, Unusual, Successful” by J. H. Kim et al., published in “S.A.E. Technical Paper Series”—“26
th
International Conference on Environmental Systems, Monterey, Calif.”—Jul. 8-11, 1996), the thermo-optical properties of the craft's radiating panels are lost because of the presence of the heaters. This imposes the use of a dedicated thermal mock-up and building the mock-up considerably increases the test preparation time and therefore the cost of the test.
SUMMARY OF THE INVENTION
The object of the invention is to provide a new method of simulating external thermal fluxes absorbed by external radiating components of a spacecraft in flight which reduces the cost and duration of thermal equilibrium tests to be reduced by carrying them out directly on the craft to be launched into space and without using a solar simulator.
According to the invention, this object is achieved by means of a method of simulating external thermal fluxes absorbed by at least one external radiating component of a spacecraft in flight, the method consisting in integrating heating means between said external radiating component and a panel carrying it and using the heating means to simulate said fluxes.
Because the heating means for simulating the external thermal fluxes are integrated between the radiating components and the panels which carry them, the particular properties of the radiating components are not disturbed by the heating means. Consequently, the heating means can be integrated directly into the flight model of the spacecraft, and no a mock-up is needed. This significantly reduces the cost and duration of the tests.
A preferred embodiment of the invention uses electrical heating means connected by electrical conductors to an external electrical power supply to simulate the external thermal flux.
The heating means are left in place when simulation of the external thermal flux is completed, the electrical conductors are cut and electrical connectors of the heating means are connected to the spacecraft earth.
The heating means are preferably integrated in a single operation during mounting of the external radiating component on the panel.
In this case a first film of adhesive, parallel heating strips forming the heating means, a second film of adhesive and the external radiating component are placed on the panel in succession and pressure is applied to the resulting assembly to bond it, for example using a vacuum vessel.
The invention also provides a spacecraft having a structure including panels of which at least one panel carries at least one external radiating component on an external face, wherein heating means used to simulate external thermal fluxes absorbed by said external radiating component in flight are permanently integrated between that component and the panel which carries it.
The heating means, which are electrical heating means in a preferred embodiment of the invention, preferably include parallel heating strips whose ends are connected together by electrical connectors beyond the peripheral edges of the radiating component.
REFERENCES:
patent: 3227879 (1966-01-01), Blau et al.
patent: 3374830 (1968-03-01), O'Sullivan, Jr.
patent: 4546983 (1985-10-01), Rosa
patent: 4726688 (1988-02-01), Ruel
patent: 4801113 (1989-01-01), Engelhardt
patent: 4802
Alcatel
Barefoot Galen L.
Sughrue & Mion, PLLC
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